1. Field of the Invention
The present invention is directed to a polarized electromagnetic relay, and more particularly to a polarized relay having a base of magnetic material which forms a part of flux path for driving an armature between two positions of opening and closing a relay contact.
2. Description of the Prior Art
Polarized relays having a base of magnetic material which forms a part of magnetic flux path are known in the art. The magnetic circuit of the prior polarized relay can be schematically illustrated in FIG. 1, in which a polarized electromagnet is mounted on the base 1 of magnetic material. The polarized electromagnet comprises an excitation coil 2, an armature 3 magnetically coupled to the base 1 through a yoke 5 and extending through the coil 2, and a pair of first and second pole members 4 and 6 magnetized to opposite polarity by an permanent magnet 7 interposed therebetween. The armature 3 is pivotally supported at its one end to the top of the yoke 5 with the other end thereof extending into a magnetic gap between the first and second pole members 4 and 6. The first pole member 4 is magnetically coupled to the base 1 so that, when the coil 2 is deenergized, a magnet flux emanating from the permanent magnet 7 circulates, as indicated by an arrow M in the figure, through the first pole member 4, the base 1, the yoke 5, the armature 3, and the second pole member 6 to thereby hold the armature 3 in an illustrated rest position of being attracted to the second pole member 6. Upon energization of the coil 2 to develop a coil flux opposing the magnet flux, the coil flux circulates, as indicated by an arrow C in the figure, through the armature 3, the yoke 5, the base 1, the first pole member 4, and through the magnetic gap between the first pole member 4 and the armature 3. The coil flux developed by the coil 2 is sufficient in strength to overpower the magnet flux of the permanent magnet 7 to thereby force the armature 3 to a set position where the other end of the armature 3 is attracted to the second pole member 6. The above magnetic structure, however, encounters a problem that as the gap between the first pole member and the armature end becomes greater, the coil flux suffers from a correspondingly increased magnetic resistance at that gap. Therefore, the coil flux must be correspondingly greater in strength enough to overcome the magnet flux of the permanent magnet at the initial movement of attracting the armature to the first pole member away from the second pole member, although it requires no such greater strength once the armature moves out of the second pole member to shorten the gap. Consequently, it is mostly desired to expedite the armature off the rest position at the beginning of the armature movement toward the set position for improving response sensitivity without unduly increasing the magnetic strength of the excitation coil.